1. Field of the Invention
The present invention relates to a reed valve and reed valve assembly suitable for supplying air to an intake system or exhaust system of an internal combustion engine (engine), and particularly to a reed valve and reed valve assembly used to supply secondary air to an exhaust port of an engine.
2. Description of the Related Art
A secondary air supply port of an engine has been used as an exhaust gas regulating counter-measure. The secondary air supply port supplies air from an air cleaner to an exhaust port to recombust an uncombusted component contained in the exhaust gas. In such a case, a reed valve is generally provided at some point in the secondary air supply unit so that exhaust gas from the exhaust port does not flow back to the air cleaner. In order to achieve this, air is supplied from the air cleaner to the exhaust port by taking advantage of a pressure difference between areas above and below the reed valve arising in the exhaust port as a result of pulsation of the exhaust gas. Specifically, when the pressure at the exhaust port side is low, the reed valve is opened to supply air from the air cleaner to the exhaust port, while when the pressure at the exhaust port side is high the reed valve is closed to prevent exhaust gas flowing back to the air cleaner.
One such reed valve has a valve hole in a central part of a plate shaped support substrate, passing through in the plate thickness direction, with a reed arranged so as to cover this valve hole. One end of the reed is fixed to a support base in the longitudinal direction, and in the case of using a secondary air supply unit the reed valve is arranged so that a surface to which the reed is attached is positioned at an exhaust port side. Japanese Patent Laid-open No. 2002-250233 disclosed an example of such a reed valve.
However, in the case of a reed valve having the above-described structure, achieving the paper plate thickness can be difficult. Excessive pressure to the reed valve can occur, such as when there us a rapid transition from a low pressure state at the exhaust port side to a high pressure state and, therefore, the plate must be thick. On the other hand, to increase followability of the reed valve the plate thickness should be thin. Accordingly, there is a need for a reed valve that can accomplish both of these conflicting requirements.